Organic polymers containing pendant --COOH groups are well known and may be prepared by various processes, e.g., as shown in U.S. Pat. Nos. 3,441,545; 3,264,269; 3,310,518; 3,361,842; 3,413,272; and 3,520,861. Typically, such polymers are prepared by polymerizing a monomer mixture comprising at least one monomer having carbon-to-carbon alpha-beta ethylenic unsaturation (e.g., olefins, vinyls, acrylates, methacrylates, and the like) with at least one monomer having not only carbon-to-carbon unsaturation but also containing at least one carboxylic acid (--COOH) group (e.g., acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, cinnamic acid, citraconic acid, succinic acid, and the like). Various copolymers terpolymers, interpolymers, oligomers, and polymer blends are known which contain pendant --COOH groups, including those which are formed by grafting the --COOH groups onto an existing organic polymer chain. It is also known to produce --COOH groups on organic polymer chains by hydrolysis of pendant ester groups on the chain, e.g., a polymer which contains ethyl acrylate as one of the monomers may be hydrolyzed, splitting off ethanol and leaving pendant --COOH groups on the polymer chain.
It is also known to convert such pendant --COOH groups to anhydride groups, (--CO--O--CO--R), where R is organic, by reaction with, e.g., an acyl halide (U.S. Pat. No. 3,523,930) or a ketene (U.S. Pat. No. 3,631,157); also as shown in U.S. Pat. No. 3,803,087 and U.S. Pat. No. 3,631,156. Furthermore, it is known (e.g. U.S. Pat. No. 3,803,087) to react nucleophiles (denoted here as NuH) having active hydrogens (or alkali metal derivatives) with said pendant anhydrides to form derivatives, denoted here as (--CO--Nu), of the anhydride groups.
The polymers having pendant anhydride groups may be reacted or crosslinked with compounds or polymers having two or more nucleophilic groups, thus forming polymers wherein two or more anhydride groups on a polymer molecule are reacted with two or more groups on a polyfunctional compound or wherein anhydride groups on different polymer molecules are reacted with nucleophilic groups on a single polyfunctional compound. Steric factors and molecular mobility will generally govern or affect which anhydride group reacts with a given nucleophilic group, it being realized by artisans that low molecular weight, low viscosity polymers (e.g., dimers, trimers, oligomers) are more mobile than higher molecular weight, more viscous polymers.